Digitizer tablets are well known input devices for computers, such as PCs. The January 1989 issue of Byte magazine, pages 162 to 174 , describe various types of commercially available tablets and the technologies employed. The basic function of a tablet is to input to the computer X/Y coordinate data representing the current location of a pointing device (stylus, pen, or cursor) on or over the tablet active area. A typical use is to trace with a cursor a diagram on the tablet, and have the diagram accurately reproduced on the display screen of the computer. But, should the display not provide an accurate replica of the diagram, the question arises as to which entity in the chain is malfunctioning. Since the entities involved include not only the tablet, but also the application program getting and using the coordinate data, the driver interfacing the tablet to the computer, as well as the computer, this is not an easy question to answer. It would be very helpful to the user to be able to pin down the problem to the tablet or to the other entities. Other than by returning the tablet to the manufacturer, there is no simple way for a user to test the tablet and establish that it is performing according to its published specifications.